It's not just the idea in isolation though. I don't think anyone would complain much if the rule was "in N mths the threshold is X". Everyone could do the necessary adjustments and play by the same rules. But if the rule applies immediately, favours the guy who gave you millions, and impacts the competition financially where they need to make me investments to comply with the rules... yeah, that stinks even if it looks like a generic rule.
Ideally that's the long term goal though, right? You want good local production, but not impair the trade forever. The best tariff would be a future one that achieves the shift by threat, then gets cancelled because the goal is complete and there's no point is impacting trade otherwise.
If companies believe today that in 4 years the tariffs will be dropped and that their investment in a manufacturing facility with 25% higher costs than the foreign competition will become effectively worthless, they will be reluctant to invest all that much.
